Ion channel modulation is a fundamental feature of dynamic electrical signalling in the brain. Voltage-dependent K channels are intimately involved in regulating neuronal activity and may be potential targets for therapeutic drugs. The specific aim of this research proposal is to study the functional consequences and structural correlates of tyrosine phosphorylation of ion channels using the cloned voltage-gated potassium channel, Kv1.3, in a heterologous expression system. Preliminary data indicate that the activity of Kv1.3, expressed in HEK 293 cells, can be modulated by co-expression of the cellular tyrosine kinase v-src or treatment with the tyrosine phosphatase inhibitor pervanadate. Biochemical data from others in the Levitan laboratory have shown that both of these treatments increase the tyrosine phosphorylation of Kv1.3. Site-directed mutagenesis and electrophysiological recordings in cDNA transfected cell lines will be combined to (1) elucidate the biophysical properties of Kv1.3 that are modulated by tyrosine phosphorylation, and (2) identify the tyrosine residue(s) whose phosphorylation is responsible for the modulation. This combined biophysical/molecular approach will provide fundamental information about the molecular details and cellular consequences of ion channel modulation in neurons and other cell types.